"Caler" in French is propping up or setting up something.
"Décaler" is to shift something, or set up two things differently, relative to each other.
"Décalage" is the amount you shift something by.
(Here endeth the French lesson.)
Never seen it applied to aircraft rigging, but makes perfect sense, as long as you qualify whether it's between upper and lower wing on a biplane, or between wing and horizontal stabiliser.